1. Field of the Invention
This invention relates to the field of signal amplification, and more particularly concerns the method and apparatus for amplifying signals from elemental detectors from a detector array.
2. Description of Related Art
Elemental infrared detectors are often used in surveillance, target seeking, and search and tracking imaging systems to sense the presence of electromagnetic radiation with wavelengths from 1-30 .mu.m. To detect infrared radiation, these elemental detectors often use temperature sensitive pyroelectric and ferroelectric materials such as triglicine sulfate and lanthanum doped lead zirconate titanate. Such crystals exhibit spontaneous electrical polarization in response to incident infrared radiation which creates a potential drop across electrodes attached to the crystals. Photoconductive materials such as lead-sulfide and mercury-cadmium-telluride may also be used in which the resistance of the material changes as a function of incident radiation. Finally, photovoltaic devices such as those fabricated from mercury-cadmium-telluride, indium antimonide, or similar materials having a standard P/N junction may be used for infrared detection. In such devices, intrinsic band-to-band electron-hole excitation generates a current or voltage which is proportional to the incident radiation flux.
Arrays of such elemental detectors may be used to form thermal imaging systems. In real-time thermal imaging systems such as forward looking infrared ("FLIR") imaging sensors, oscillating prism mirrors are used to scan radiation emitted by a source across a one-dimensional array of elemental detectors. When the elemental detectors are used in this manner, the temporal outputs of the detectors may be used to generate a two-dimensional representation of the image. In two-dimensional detector array imaging systems which can utilize either staring or scanning arrays, the elemental detectors produce free charge carriers or currents which may then be monitored by an appropriate readout integrated circuit such as a charge-coupled device ("CCD"). The output from the CCD can be processed by various techniques such as time delay integration and parallel-to-serial scan conversion, with the choice depending on the system requirements of frame rate, signal-to-noise ratios, etc. Other readout devices may also be used.
The outputs from detector arrays are typically delivered to a plurality of amplifiers, each of which may include a preamplifier and a postamplifier. In the case of impedance photoconductors such as those using low wavelength mercury-cadmium-telluride, a low-power/low-noise amplifier is required which is typically connected to a temperature and voltage stable detector bias voltage regulator. However, such amplifiers often have much relatively poor rejection of power and common mode noise. In addition, the fact that such amplifiers often have relatively large power consumption tends to limit the number of amplifiers which can be placed on a single chip. For example, the OP 27 amplifier can not be used in integrated detector packages where a relatively high number of amplifiers are required.